The present invention relates to the treatment or prevention of vascular proliferative disorders, such as restenosis following angioplasty or other vascular trauma. The invention also relates to treatment or prevention of other disorders, such as benign or malignant cancers. Microcapsules containing an active inner core and a protective outer shell capable of delivering a therapeutic dosage of radiation or other active agent are delivered directly to a treatment site.
Vascular proliferative disorders are conditions within the walls of blood vessels, including arteries and veins, which result in occlusion or blockage of blood flow. These conditions may result from injuries or wall alterations incurred during surgical intervention, for example during angioplasty, atherectomy, graft or shunt implantation, or coronary by-pass surgery.
One common vascular proliferative disorder is stenosis of coronary arteries due to the build-up of atherosclerotic plaque on the arterial wall. Several minimally invasive procedures such as balloon angioplasty have been developed to allow the lumen of the vessel to be reopened or enlarged. One of the chief problems with treatment by mechanical dilatation is that restenosis of the vessel generally occurs due to smooth muscle cell proliferation or the occurrence of intimal hyperplasia.
Treatment of such sites with radiation is believed to be effective in decreasing restenosis. One such method of radiotherapy is implantation of a stent containing a radioisotope source at the site of the stenosis. For example, U.S. Pat. No. 5,059,166 to Fischell et al. discloses a stent where the radioisotope source is contained either in the surface coating of the stent or in the metal alloy that forms the stent. Two primary limitations on the use of such stents are that the dosage of the stent cannot be increased or decreased once it has been implanted, and that current stents are as a practical matter permanent implants that remain in place for the lifetime of the patient.
Another method of radiotherapy is the use of a radioactive catheter or wire. For example, U.S. Pat. No. 5,199,929 to Dake et al. discloses a catheter with a radioisotope source permanently attached to the distal end. The primary limitations on the use of such devices are that the source of radiation is not in uniform radiation delivery contact with all of the surfaces that require treatment and that treatment continues only as long as the catheter remains in the patient's body.
Thus, a need remains for an improved method and devices to effect a site-specific treatment for vascular proliferative disorders. There also remains a need for methods and devices to treat other conditions, such as cancer and cellular disorders, which are believed to benefit from localized radiation exposure.